1. Technical Field
This invention relates to a semiconductor laser device using a solid and a method of manufacturing the same.
2. Prior Art
Compound semiconductor laser devices are popularly used as solid-state semiconductor light emitting devices in the field of optical telecommunication and other optical technologies.
Semiconductor laser devices used for these applications are normally provided with a feature of confining the electric current running therethrough in order to reduce the threshold current level when starting laser oscillation.
FIG. 9 of the accompanying drawings schematically illustrates a semiconductor laser device having such a current confinement feature.
A semiconductor laser device as illustrated in FIG. 9 comprises an n-InP lower clad layer 12, an n-InGaAs active layer 13, a p-InP upper clad layer 14, a p-InP layers 15, an n-InP layers 16, said p-InP layers 15 and n-InP layers 16 being provided as electric current blocking layers, a p-GaInAsP contact layer 17 and an insulation layer 18 arranged on an n-InP substrate 11 in the above-mentioned order to form a multilayered structure, on the upper and lower surfaces of which a p-electrode 19 and an n-electrode 10 are respectively mounted.
A semiconductor laser device having a structure as shown in FIG. 9 is produced through a process as described below.
In the first step of crystal growth operation, the n-InP lower clad layer 12, the n-InGaAs active layer 13 and the p-InP upper clad layer 14 are sequentially formed on a substrate 11 by means of an MBE technique and thereafter the obtained intermediary multilayered structure is etched at a predetermined location to narrow the active layer 13.
Then, in the second step of crystal growth operation, the p-InP layer 15 and the n-InP layer 16 are sequentially formed as electric current blocking layers on the intermediary multilayered structure by means of an LPE technique.
Finally, in the third step of crystal growth operation, the p-InGaAs contact layer 17 is formed atop by means of an MBE technique.
A semiconductor laser device produced in a manner as described above can effectively confine the electric current running therethrough by utilizing the current blocking layers 15 and 16 of the pn reverse junction type formed on the opposite lateral sides of the active layer 13.
Another semiconductor laser device also having a current confinement feature is illustrated in FIG. 10.
A semiconductor laser device as illustrated in FIG. 10 comprises an n-InP lower clad layer 22, an n-InGaAs active layer 24 having its upper and lower surfaces covered by respective GaAs buffer layers 23 and 25, an Si-doped n-AlGaAs upper clad layer 26, a GaAs contact layer 27 and an SiO.sub.2 insulation layer 28 arranged on a p-GaAs substrate 21 in the above mentioned order to form a multilayered structure, on the upper and lower surfaces of which an n-electrode 29 and a p-electrode 20 are respectively mounted.
The p-GaAs substrate 21 of the semiconductor laser device of FIG. 10 has different surface levels as it has a mesa between a pair of flat and low side areas.
The flat surface of the highest central area of the mesa has a (100) plane, whereas the lateral slopes of the mesa connecting the higher level and the lower level have a (311) A plane.
Since the dopant Si of the n-AlGaAs upper clad layer 26 of the semiconductor laser device of FIG. 10 is an amphoteric impurity substance, the (100) plane of the layer is of n-type, whereas the (311) A plane of the layer is of p-type.
With such an arrangement, a pn junction is formed within the Si-doped n-AlGaAs upper clad layer 26 to block any transversal electric currents that may flow therein.
Besides, the electric current confinement structure of the semiconductor laser device illustrated in FIG. 10 can be formed by a single epitaxial growth operation.
3. Problems to be Solved by the Invention]
Semiconductor laser devices such as those illustrated in FIGS. 9 and 10 are accompanied by the following problems that remain unsolved.
(1) A mesa etching step is inevitably required in the process of crystal growth for forming the layers of a semiconductor laser device as illustrated in FIG. 9. This means that the process of crystal growth needs to be interrupted, consequently making the operation of controlling the overall process of manufacturing such a semiconductor laser device rather complicated. PA1 (2) The use of a different material for a semiconductor laser device as illustrated in FIG. 19 inevitably results in the failure of providing it with a current confinement feature.
For instance, if an InAlAs clad layer and an InGaAs active layer are formed on an InP substrate having different surface levels, while the (100) plane of the substrate is turned to n-type by doping the InAlAs clad layer with Si, the (111) A plane that needs to become p-type is also turned to n-type having a degree of carrier concentration similar to that of the (100) plane.
Thus, a current confinement operation cannot be successfully carried out by means of pn junction if a laser structure is formed on the (100) plane of the InP structure that also has a (111) A plane or a (311) A plane.
In view of the above described technological problems, it is therefore an object of the present to provide an advanced high-quality semiconductor laser device having a current confinement feature as well as a method of manufacturing the same in a simple manner.